In order to mark a cable in this way using a laser, German Pat. No. 3,147,230 describes a cable whose outer surface is initially sprayed with a colored coating which is baked using high-frequency waves or infra-red waves and which is subsequently burned using laser radiation. However, this document is concerned solely with the surface burning obtained by the laser radiation.
U.S. Pat. No. 4,370,542 claims cable marking by means of a laser, but it relates, in fact, solely to the relative positioning of the cable and the laser source.
There exist other prior art documents relating to marking various types of surfaces for identification purposes (e.g. plastics), or else for preparing stencils or lithographic plates. In some of these documents, and in particular in European Pat. No. 159,529 and French Pat. No. 2,520,902, the marking technique makes use of two surface layers, one of which absorbs laser radiation while the other, outer layer, is transparent.
U.S. Pat. No. 3,505,916 proposes distinguishig two insulated conductors by means of two successive layers of insulation having different colors. This document describes identifying insulated conductors by mechanically cutting a spiral in the outer layer of each conductor, with the cut exposing an underlayer which contrasts relative to the outer layer. However, such a method is incapable of putting genuine inscriptions on a conductor.
In contrast, the present invention seeks to provide a special disposition for the outer layer of an electric cable enabling it to be marked by a laser beam.